1. Field of the Invention
The invention pertains generally to electronic fuel injection systems for internal combustion engines and is more particularly directed to a fuel schedule delivery system for multiple fuel injectors at a single injection point.
2. Description of the Prior Art
With the increasing need for more precise control of fuel mixtures to internal combustion engines, many in the art have turned to electronic fuel management systems for the answer. These electronic fuel management systems compute the basic fuel needs of the internal combustion engines and control the fuel delivery by opening and closing one or several solenoid operated fuel injectors. Generally, a computation is made of the desired amount of fuel and a variable length electrical pulse is supplied to the coil of the injector to open it for a duration equivalent to the quantity necessitated.
These electronic fuel management systems have been used successfully in single and multi-point type systems. In a multi-point system each cylinder or distribution point has a separate controllable injector which may be fired sequentially, simultaneously, or in a combination of modes with the other injectors, whereas in a single point system, a plurality of injectors is found at a single ingestion point, typically the throttle body or the intake manifold of the engine. However, multiple injectors for each ingestion point in multi-point systems are becomming more common because increased accuracy can be obtained with more than one injector per cylinder.
There have been some problems encountered with utilizing multiple injectors at a single point, in that to match the fuel schedule requirements of the engine and emission standards, several different size injectors have been used. Precision small injectors are necessitated in the so-called emissions operating range of engine conditions to provide the best accuracy of fuel delivery and larger injectors are used in the so-called power operating range of engine conditions where large fuel deliveries are required. Different injectors of different sizes are burdensome to match to the fuel schedule and switchover problems can create inaccuracies in the fuel delivery.
The multiple injectors are also difficult to control when the engine reaches the border conditions where the small injectors have to be shut off and the large injectors are turned on. When the engine operates approximately at the switching point, this condition may cause some instabilities in the system as it tries to switch back and forth or oscillate between the two sets of injectors. One such system that discloses the use of a hysteresis characteristic to overcome this boundary condition is a U.S. Pat. No. 4,002,152 issued to Hoshi, Jan. 11, 1977. However, by using this hysteresis condition, the system will not follow the fuel delivery schedule with a great amount of precision around the operating point, required to accurately control emissions.
Another factor to be considered is that in multiple injector single-point systems the fuel preparation changes abruptly as the cross-over is reached and therefore the spray patterns are not the same with the different sizes of injectors. This can cause considerable inaccuracy between the amount of fuel actually delivered and the fuel schedule amount determined by the feedback control system.